This invention relates to a solar-heat collecting apparatus. The solar-heat collecting apparatus can be broadly divided into the conventional indirect conversion system employing selective heat absorption membrane, the direct conversion system in which a substance having excellent heat absorption characteristics is used as the heat absorbing fluid, based on a new concept, to which fluid the sun-rays are directed directly to collect the heat thereof, and the heat pipe system etc.
However, the indirect conversion system is based on the principle that the heat collected by the selective heat absorption membrane is transmitted by heat conduction to the fluid and is not so high in efficiency and is also disadvantageous in terms of cost because it requires a considerably high cost in manufacturing the selective heat absorption membrane.
Whilst, the heat pipe system is higher in cost than the indirect conversion system and it is difficult to say that the system is commercially payable.
In contrast thereto, in the case of the direct conversion system, the solar-heat is absorbed directly by the heat absorbing fluid and therefore there is no room for causing the heat losses due to heat transfer etc. which take place in the indirect conversion system.
The solar-heat collection efficiency of this direct conversion system depends largely on the characteristics of the heat absorbing fluid. Preferred examples of the heat absorbing fluid are those disclosed in the Japanese Patent Application No. 56-108854 and the corresponding U.S. application Ser. No. 397,983, filed on the July 14, 1982, issued as U.S. Pat. No. 4,482,467 on Nov. 13, 1984, and assigned to the common assignee of the present application.
The heat-absorbing fluid disclosed in the Japanese and U.S. application comprises:
(a) a dispersing medium selected from the group consisting of propylene glycol, mixture of propylene glycol with water, mixture of propylene glycol with water and glycerin, and mixture of glycerin with water, PA0 (b) a dispersant selected from the group consisting of polyvinylpyrrolidone, caramel, and mixture of polyvinylpyrrolidone with caramel, and PA0 (c) a powdered activated carbon as a black coloring material.